1. Field of Invention
The present invention relates to a heat pump type air conditioner and a method for controlling a heat pump type air conditioner.
2. Description of Related Art
Conventional air conditioners have an outdoor fan blowing outdoor air through an outdoor heat exchanger. In the air conditioner, the rotational speed of the outdoor fan is controlled in order to improve the heat exchange efficiency and to prevent an excessive pressure from developing in the refrigeration circuit.
Recently, air conditioners with an inverter controlling the rotational speed of a compressor have been developed. In these air conditioners, the rotational speed of the outdoor fan is controlled based on the compressor rotational speed, that is the output frequency of the inverter. For example, when the compressor rotational speed is high, a large amount of refrigerant flows in the outdoor heat exchanger. Under this condition, more air must pass through the outdoor heat exchanger. Therefore, when the compressor rotational speed is high, the rotational speed of the outdoor fan is set high. Conversely, when the compressor rotational speed is low, the outdoor fan rotational speed is set low. By this outdoor fan speed control, high heat exchange efficiency can be obtained and wasteful power consumption can be avoided.
This outdoor fan control can be used in a heat pump type air conditioner which is able to operate in both a cooling mode and a heating mode. The outdoor fan speed is controlled according to a flow-chart shown in FIG. 8. After the air conditioner starts, the outdoor fan control circuit determines whether the compressor rotational speed, or the inverter output frequency f, is more than 40 Hz (step S1). If it is more than 40 Hz, the outdoor fan is operated at a "High"0 speed (step S2). If not, the outdoor fan is operated at a "Low" speed (step S3). The threshold value of 40 Hz is usually determined as the reference in the heating mode, which requires a greater air conditioning capacity, and the outdoor air flow during "High Speed" or during "Low Speed" is set so that the heating operation efficiency will be high.
However, recently, efforts have been made to improve energy-savings and operating efficiency (COP). However, control of the outdoor air flow, that is, control of the outdoor fan speed, has simply followed the prior art control pattern described above.
Thus, despite the fact that a heat pump can operate in either a cooling mode or a heating mode, nothing other than switching between "High Speed" and "Low Speed" has occurred, taking the specified compressor rotational speed of 40 Hz as a reference value.